裂纹宽度对岩石断裂韧性测试结果的影响

深部地层岩石的断裂韧性是水力压裂设计和数值模拟中的一个重要参数。通过试验分析和有限元数值计算 ,研究了试件的裂缝宽度对应力强度因子的影响 ,给出了确定无因次应力强度因子与裂尖半径关系的数值方法 ,弥补了解析方法中裂缝零宽度假设的不足。研究结果表明 ,当裂缝宽度较小时 ,解析方法可以用于计算断裂韧性 ;当裂缝宽度较大时 ,采用解析方法计算出的断裂韧性偏差较大。试验测定时 ,应使裂尖半径尽可能小 ,并且破裂压力应该与裂尖半径相对应。这为正确确定岩石的断裂韧性提供了可靠的理论依据和试验方法

Influence of fracture width on rock toughness measurement

The toughness of the underground rock in deep formation is an important parameter in the numerical simulation of hydraulic fracturing treatment, and its value is usually determined under laboratory conditions. The finite element analysis and experimental means were employed to investigate the influence of pre fracture width on the stress intensifying factors. A method for determining the relationship of dimensionless stress and intensity factors with the radius of fracture tip was proposed, which is the complementary part to the analytical procedures. The experiment proved that the analytical procedures are usable to calculate the toughness only when the radius of fracture width is small, due to their ineffectiveness to deal with the problems beyond fracture mechanics. And it is required that the failure pressure should be taken as an input of calculation corresponding to the real magnitude of radius of fracture tip. The conclusions provide the theoretical grounds for correctly determining the toughness of rock fracture, as well as for the reliable experimental specimens.